Roy Moore, hoping to be elected to represent Alabama in the US Senate in December

US President Donald Trump would expect Senate candidate Roy Moore to withdraw from an upcoming vote if allegations that he had a sexual encounter with a 14-year-old girl were true, the White House said on Friday.

"Like most Americans the president believes we cannot allow a mere allegation, in this case one from many years ago, to destroy a person's life," Ms Sanders told reporters aboard Air Force One before Trump arrived in Vietnam to attend an Asia-Pacific summit.

"However, the president also believes that if these allegations are true, Judge Moore will do the right thing and step aside."

On Thursday an Alabama woman, Leigh Corfman, now 53, alleged that Mr Moore approached her in 1979 outside a courtroom in Etowah County, Alabama, as she was sitting on a wooden bench with her mother.

As her mother went inside he asked for her phone number and called twice to pick her up and take her to a house.

She told the paper that she felt flattered that a grown man was paying attention to her.

“He was charming and smiley,” she said. “I was kind of giddy, excited, you know? An older guy, you know?”

The first time they met, he picked her up in his car.

“I remember the further I got from my house, the more nervous I got,” she said.

She recalled telling him she was 14, and they kissed before she asked to be taken home.

The second time they went to the same house.

Nigel Farage campaigning for Roy Moore in Alabama on September 25

“This was a new experience, and it was exciting and fun and scary. It was just like this roller-coaster ride you’ve not been on,” she said.

She alleges that Mr Moore left the room and returned wearing only his underwear, then kissing her and taking off her trousers and shirt and touching her through her clothes. He then guided her hand to his underwear, at which point she pulled her hand back and said she wanted to leave.

“I wasn’t ready for that — I had never put my hand on a man’s penis, much less an erect one,” she said.

Two of Ms Corfman’s childhood friends say she told them at the time that she was seeing an older man, and one said Ms Corfman identified the man as Mr Moore.

Roy Moore with his wife Kayla

Nancy Wells, Ms Corfman’s mother, told the paper that her daughter told her about the encounter more than a decade later, as Moore was becoming more prominent as a local judge.

Ms Corfman never went to the police, and the statue of limitations has expired.

Aside from Ms Corfman, three other women interviewed by The Washington Post in recent weeks claimed that Mr Moore pursued them when they were between the ages of 16 and 18 and he was in his early 30s. They said they found the episodes flattering at the time, but troubling as they got older.

None of the women say that Moore forced them into any sort of relationship or sexual contact.

In 1985, at age 38, he married Kayla Kisor, who was 24. The two are still married and have four children and five grandchildren.

Mr Moore has dismissed the allegations, describing them as “fake news”.

“Judge Roy Moore has endured the most outlandish attacks on any candidate in the modern political arena, but this story… takes the cake,” he said in a statement.

“These allegations are completely false and are a desperate political attack by the National Democrat Party and the Washington Post on this campaign.”

Roy Moore

But Mitch McConnell, leader of the Republican party, said: “If these allegations are true, he must step aside.”

Susan Collins, Republican senator for Maine, said: "If there is any truth at all to these horrific allegations, Roy Moore should immediately step aside as a Senate candidate."

Pat Toomey, senator for Pennsylvania, said: “All I️ can say is, if there’s a shred of truth to it, then he needs to step aside.”

Lisa Murkowski, senator for Alaska, said she was"horrified", adding: "If it's true he should step down immediately."

John McCain went further and said Mr Moore should step aside “immediately”.

“The allegations against Roy Moore are deeply disturbing and disqualifying,” he said.

“He should immediately step aside and allow the people of Alabama to elect a candidate they can be proud of.”

Some Alabama Republicans jumped to his defence, though.

Paul Reynolds, the Republican National Committeeman from Alabama, told The Hill: “My gosh, it's The Washington Post. If I’ve got a choice of putting my welfare into the hands of Putin or The Washington Post, Putin wins every time,” he said.

“This is going to make Roy Moore supporters step up to the plate and give more, work more and pray more."

Jim Zeigler, the state auditor and a longtime supporter of Mr. Moore, said there was "nothing to see here".

“Single man, early 30s, never been married, dating teenage girls. Never been married and he liked younger girls," he said, according to the New York Times. "According to The Washington Post account he never had sexual intercourse with any of them.”